Chemiluminescence may be simply defined as the chemical production of light. In the literature it is often confused with fluorescence. The difference between these two phenomena lies in the source of the energy which promotes molecules to an excited state. In chemiluminescence this source is the non-radiative energy yielded as the result of a chemical reaction. The subsequent decay of molecules from the excited state back to the ground state is accompanied by emission of light, which is called luminescence. In contrast, in fluorescence, incident radiation is the source of the energy which promotes molecules to an excited state.
The history of chemiluminescence, especially that occurring in the non-aqueous phase, is remarkably short. The important aqueous chemiluminescent substances luminal and lucigenin were discovered in 1928 and 1935, respectively. A series of organic soluble chemiluminescent materials were developed in the early 1960's based upon a study of the luminescent reactions of a number of oxalate compounds. A typical organic system useful for chemiluminescence was disclosed by Bollyky et al., U.S. Pat. No. 3,597,362 and claimed to exhibit a quantum efficiency of about 23% compared with about 3% for the best known available aqueous systems.
The two-part peroxy-oxalate chemical lighting systems known in the prior art provide practical chemical lighting systems that are useful for a variety of applications. These systems are efficient producers of chemiluminescent light, are storage stable, simple to operate, safe to use, and are capable of being formulated to meet a variety of brightness, color and lifetime requirements. Examples of these prior art chemiluminescent lighting systems can be found in one or more of the following U.S. Pat. Nos. 3,749,679; 3,391,069; 3,974,368; 3,557,233; 3,597,362; 3,775,336; and 3,888,786, which are incorporated herein by reference.
The production of devices capable of emitting light through chemical means is well-known in the art. LIGHTSTICKS, for example, are taught in U.S. Pat. No. 3,539,794, while other configurations have also been the subject of many U.S. Pat. Nos. e.g. 3,749,620; 3,808,414; 3,893,938; 4,635,166; 4,814,949 and 5,121,302.
Typically, these devices comprise a particular type of packaging whereby the two components of the light producing chemical reaction are kept separate until contacting of the components is desired, at which time the two components are mixed to produce chemical light by reaction. Generally, the two components employed in a chemiluminescent light device are (1) a component containing a chemiluminescent compound and (2) a component containing an activator compound.
The two component systems generally contain a chemiluminescent component that is a liquid phase oxalate ester which is termed the "oxalate component" and comprises an oxalate ester and a solvent; and an "activator component" which contains hydrogen peroxide and a solvent.
The most commonly used activator solvents are phthalate compounds such as dimethyl phthalate and dioctyl phthalate. See e.g. U.S. Pat. Nos. 4,717,511; 4,017,415; 4,698,183 and 4,508,642. Other useful activator solvents are water, alcohols, ethers such as diethyl ether, diamyl ether, tetrahydrofuran, dioxane, dibutyldiethyleneglycol, perfluoropropylether, and 1,2-dimethoxyethane and esters such as ethyl acetate, ethyl benzoate and propyl formate.
In addition to the oxalate component and activator component an efficient fluorescer compound is included in one of the component solutions and any necessary catalyst for enhancing intensity and lifetime control must also be contained in one of the component solutions.
The oxalate component provides an oxalate ester/solvent combination that permits suitable ester solubility and also permits storage stability. The peroxide component provides a hydrogen peroxide/solvent combination that permits suitable hydrogen peroxide solubility and also permits storage stability. It is permissible that the solvents for the two components be different provided that they are miscible. It is thus necessary that at least one of the solvents solubilize the fluorescer material and at least one solvent should solubilize an efficient catalyst material. The constituents are optimally selected so as to accommodate their formulation into two reactive components which separately have extended storage stabilities and which generate useful life when combined.
Selection of solvents for each component is therefore critical in terms of safety as well as in terms of performance and storage stability. The constituents must be selected so as to maximize light output, provide products exhibiting low toxicity, low freezing point and high flash point thus providing for safe operation over an extended range of temperature. These properties are determined to a large extent by the solvent or solvents which are selected for the two reactive components in that the solvent may constitute substantially more then 90 percent of the combined system. In this regard, the present applicants have discovered that the use of triethyl citrate as an activator solvent unexpectedly provides increased overall light output and a "flatter" production of light during the lifetime of the device. Additionally, it has been discovered that inclusion of a sodium perborate/salicylic acid catalyst improves the characteristics of chemiluminescent systems in general, and particularly improves those utilizing a triethyl citrate activator solvent.
Prior Patents:
U.S. Pat. No. 4,508,642 discloses a method of obtaining greater lifetime duration from chemiluminescent systems by utilizing ditridecyl phthalate (DTDP) or ditridecyladipate (DTDA) in liquid chemiluminescent systems based upon a chemical reaction involving an ester of oxalic acid mixed with an organic fluorescer, hydrogen peroxide, and a catalyst. Admixing of the DTDP or DTDA in the chemiluminescent system produces a greater light output coupled with a greater lifespan for said chemiluminescent system.
WO 94/19421 discloses a phthalate free chemiluminescent activator solution. The International application describes an activator component solution comprising a peroxide compound in a solvent which is selected from the group consisting of acetyl trialkyl citrates, trialkyl citrates, N-alkyl-arylenesulfonamides, dialkyl adipates, pentaerythritol tetrabenzoate, glyceryl tribenzoate and mixtures thereof. The application further discloses a catalyst system and a chemiluminescent component comprising an oxalic acid ester and an organic fluorescer.